1. Field of the Invention
The present invention relates to an electronic device having functionality and to a production method of the electronic device. Specifically, the present invention relates to an electronic device including a semiconductor film, an organic film, an insulating film, etc., and to a production method of the electronic device. Further, the present invention relates to a plasma process apparatus for forming a thin film of semiconductor, conductor, or the like. Specifically, the present invention relates to plasma process apparatuses, such as a plasma chemical vapor deposition apparatus using a plasma-activated chemical vapor deposition method, which is used for forming a thin film of semiconductor, conductor, or the like, a dry etching apparatus used for forming a thin film pattern of a semiconductor film or conductor film, and an asher apparatus for removing a resist used in the formation of a thin film pattern.
2. Description of the Prior Art
A method for forming a semiconductor film, or the like, using plasma in the production of an electronic device, such as an integrated circuit, a liquid crystal display, an organic electroluminescence device, solar cell device, or the like, i.e., a so-called plasma-activated chemical vapor deposition (plasma-activated CVD) method, is advantageous because of its convenience and usability and therefore has been employed in the production of various electronic devices.
An embodiment of an apparatus using a plasma CVD method (a plasma chemical vapor deposition apparatus; hereinafter, referred to as “plasma CVD apparatus”) illustrated in FIGS. 33 and 34 has been commonly employed in the art. The plasma CVD apparatus is now described with reference to FIGS. 33 and 34. FIG. 33 is a general view of a conventional plasma CVD apparatus. FIG. 34 is a schematic cross-sectional view of the conventional plasma CVD apparatus. The plasma CVD apparatus includes a closed space realized in the form of a process chamber (vacuum container) 5 and two conductive plates 2a and 2b contained in the process chamber 5 which are electrically insulated from each other and positioned in parallel so as to face each other. Plasma 11 is produced in an area between the conductive plates 2a and 2b, and a source gas is then introduced into the area so that the gas is decomposed or dissociated. As a result, a semiconductor film, or the like, is formed on a substrate 4 to be processed (target substrate 4) which is made of silicon, glass, or the like, and provided on the electrode 2b. 
Commonly employed means for producing the plasma 11 that decomposes the source gas for forming a film is electric energy such as a radio frequency wave of 13.56 MHz, for example. The conductor electrode 2b has a ground potential, and the voltage is applied to the opposite electrode 2a, whereby an electric field is produced therebetween. A glow discharge phenomenon caused by a dielectric breakdown phenomenon of the electric field produces the plasma 11. The electrode 2a to which the voltage, i.e., electric energy, is applied is referred to as a cathode electrode or discharge electrode. Since a large electric field is produced in the vicinity of the cathode electrode 2a, electrons in the plasma 11 are enhanced by the electric field, and the enhanced electrons accelerate dissociation of the source gas, whereby radicals are generated. In FIG. 34, arrows 12 represent flows of radicals.
A part of discharging area (plasma) 11 in the vicinity of the cathode electrode 2a, in which a large electric field is produced, is referred to as a cathode sheath portion. The radicals generated in the cathode sheath portion or in the vicinity thereof are diffused up to the target substrate 4 provided on the ground potential electrode 2b and deposited over the surface of the substrate 4 so as to grow a film. The electrode 2b having the ground potential is referred to as an anode electrode 2b. Another electric field having a certain size is produced in the vicinity of the anode electrode 2b and is referred to as an anode sheath portion. Hereinafter, an apparatus for forming a film on the target substrate 4 placed on the anode electrode 2b by producing plasma between the two electrodes 2a and 2b that are positioned in parallel to each other is referred to as “parallel plate type apparatus”.
Such a plasma CVD method has been widely employed in the production of electronic devices in various industries. For example, in a production process of an active liquid crystal display, a switching element called a TFT (Thin Film Transistor) is fabricated. In the TFT, a gate oxide film, such as an amorphous silicon film, a silicon nitride film, or the like, is an important constituent. In order to achieve desired effects of the respective films of the TFT, a technique for efficiently forming a transparent high quality insulating film is indispensable. Further, an indispensable technique for the fabrication of an organic electroluminescence device is, for example, a technique for efficiently forming, on an organic thin film, a high quality transparent insulating film as a protection film for protecting the surface of the organic thin film so as not to be exposed to the atmosphere. Further still, an indispensable technique for the fabrication of a solar cell device is, for example, a technique for efficiently forming, on a solar cell layer, a high quality film as a protection film for protecting the surface of the solar cell layer so as not to be exposed to the atmosphere. The thus-fabricated electronic devices have been widely used in various applications.
The apparatuses generically known as plasma process apparatuses includes a dry etching apparatus for etching a thin film and an asher apparatus for removing a resist, wherein an etching gas is used in place of a source gas and plasma is produced in the same way as in the plasma CVD apparatus. Production of the plasma 11 and generation of radicals are achieved by the same mechanisms as those employed in the plasma CVD apparatus. Radicals that reach the target substrate 4 remove a thin film, or the like. The dry etching apparatus and the asher apparatus are different from the plasma CVD apparatus only in that not only the radicals but also physical sputtering by ion impact from plasma and energy applied to the target substrate 4 are utilized in the etching process.
Conventionally established plasma CVD apparatuses possess various limitations. When the conventional CVD apparatus is used in the production of a large surface electronic device, such as a liquid crystal display, an amorphous solar cell device, or the like, it is sometimes difficult to achieve sufficient dissociation of the source gas and form a high quality thin film on the target substrate 4. For example, in a conventionally known parallel plate type apparatus, dissociation of the source gas is sometimes insufficient. In the case where a silicon nitride film is formed, silane (SiH4), ammonium (NH3), nitrogen (N2), hydrogen (H2), etc., are used as the source gas, and nitrogen which constitutes the film is obtained by decomposing ammonium. However, for example, in the case where the silicon nitride film is formed on a copper wiring, there is a possibility that ammonium gas corrodes the copper.
Ammonium gas has a strong chemical activity, and therefore, in some cases, a silicon nitride film should be formed using only nitrogen gas without using ammonium gas. In such a case, the parallel plate type apparatus cannot sufficiently decompose hydrogen gas and nitrogen gas, which are unlikely to be dissociated, and therefore, it is difficult to obtain a silicon nitride film having desirable insulating film characteristics and protection film characteristics. In the case where an amorphous silicon film is formed, silane, hydrogen, etc., are used as the source gas, but conventionally, the gas use efficiency is only about 10%. That is, it is understood that, also in this case, the parallel plate type apparatus cannot sufficiently accelerate dissociation of the source gas.
Conventional techniques for forming a high quality film on the target substrate 4 are disclosed in the documents described below.
For example, in a plasma apparatus disclosed in Japanese Unexamined Patent Publication No. 11-144892, a discharge electrode, which faces a glass plate, is formed by a plurality of electrodes. The electrodes are positioned such that radio frequency voltages having different polarities are applied to the electrodes so as to produce an electric discharge in a lateral direction. A reaction gas is supplied though an area between the electrodes. The gas supplied into the discharge plasma of lateral electric field undergoes a plasma reaction and then is diffused toward and deposited on the glass substrate. In this way, a high quality film is formed without causing discharge damage on the glass substrate. However, this plasma apparatus also cannot accelerate dissociation of the source gas.
A technique for accelerating dissociation of the source gas is disclosed in, for example, Japanese Unexamined Patent Publication No. 1-279761. In a plasma apparatus disclosed in this publication, a concave space is provided in a cathode electrode, and this concave space causes the hollow cathode effect so that the plasma density is increased. As a result, dissociation of the source gas is accelerated, and a faster film formation rate is achieved as compared with general parallel plate type apparatuses. However, in this apparatus, the surface of the target substrate is exposed to the plasma so that a surface of the substrate on which a film is formed is subjected to plasma damage.
Such a plasma damage can be repaired with heat energy by setting the temperature of the target substrate 4 to 300° C. or higher. However, when the temperature of the target substrate 4 is set to 200° C. or lower, a desirable film quality cannot be maintained. That is, a method for forming a high quality film by a plasma CVD apparatus with high gas dissociation efficiency especially at a low target substrate temperature has not yet been established.
Now, consider a case where the structure of the plasma apparatus disclosed in Japanese Unexamined Patent Publication No. 11-144892 is applied to a dry etching apparatus or an asher apparatus. Also in this case, a plasma production section and an ion impact control section are separately controlled. Specifically, a third electrode is attached to the back surface of the substrate 4 so as to control ion impact independently of plasma generation. Therefore, the controllability of parameters is increased.
However, also in this case, dissociation of a process gas is not accelerated, and accordingly, the process speed does not exceed a certain level. That is, a high performance plasma process apparatus which operates with high gas dissociation efficiency has not yet been established.
The thin films formed using the above techniques do not have sufficient protection film characteristics for use as devices. For example, in an organic electroluminescence device, it is necessary to provide a transparent, insulating protection film as an outermost layer of the electroluminescence device in order to prevent introduction of water vapor and oxygen from the atmosphere. Since the characteristics of an organic film in the device significantly deteriorate at the process temperature of 100° C. or higher, it is necessary to set the process temperature to a temperature lower than 100° C. during the formation of the protection film.
However, in the conventional plasma CVD apparatuses, a protection film having a desirable quality is not formed with such a temperature condition. For example, Applied Physics Letters, volume 65, pages 2229–2231 reports that, in the case where a silicon nitride film is formed as a protection film at 100° C., the quality of the silicon nitride film is poor so that water vapor contained in the atmosphere penetrates into the film, and silicon and oxygen are bonded. It is estimated from this report that water vapor and oxygen finally penetrate through the film. In a currently employed production method, another glass substrate is sealingly attached as a cap over the device in a nitrogen atmosphere for separation from the atmosphere because the quality of the protection film is poor. Devices which use a silicon nitride film as a protection film include a polysilicon solar cell device and a gallium/arsenic electronic device. These devices also suffer from the above described quality problems.
The present invention was conceived in view of the above problems. An objective of the present invention is to improve the quality of an electronic device by accelerating decomposition and dissociation of a gas with plasma such that the efficacy of the plasma process is increased.